Interpretive Summary: Methyl bromide (bromomethane, MeBr), which originates from the oceans, fumigation, and a few other sources, is reportedly contributing to the ozone depletion in the stratosphere. Due to the unique importance of this fumigant in soil sterilization, it is of particular interest to accurately quantify the input to the total atmospheric MeBr arising from agricultural uses, and develop approaches to minimize it. In this study, we demonstrate that application methods had drastic effect on MeBr transport in soil and the ultimate volatilization from the soil surface. We found that both surface tarping and deep injection increased MeBr retention ratio and time in the soil, leading to reduced volatilization. To minimize MeBr volatilization loss into the air, MeBr should be injected at great depths under tarped conditions. Untarped shallow applications result in maximum volatilization losses, and therefore should be avoided.

Technical Abstract:
Methyl bromide (bromomethane, MeBr), which originates from the oceans, fumigation, and a few other sources, is reportedly contributing to the ozone depletion in the stratosphere. Due to the unique importance of this fumigant in soil sterilization, it is of particular interest to accurately quantify the input to the total atmospheric MeBr arising from agricultural uses, and develop means to minimize it. In this study, we determined the effect of two important application variables, surface tarping and injection depth, on MeBr transport and transformation in soil and its volatilization from the soil surface. We found that both surface tarping and deep injection increased MeBr retention ratio and time in the soil, leading to more extensive degradation of MeBr to Br- and resulting in reduced volatilization. To minimize MeBr volatilization loss into the air, MeBr should be injected at great depths under tarped conditions. Untarped shallow applications result in maximum volatilization losses, and therefore should be avoided.